The illegal party drug ketamine could relieve the misery of millions of migraine sufferers, experts claim.

The horse tranquilliser, known as Special K by clubbers, may be an effective treatment for those who fail to respond to other medications, according to the findings of a new study.

Migraine is the third most common condition in the world affecting around one in five British women and around one in 15 British men.

The findings of the study, based on 61 male migraine sufferers in their 40s admitted to the hospital over a period of three years, have been presented at the ANESTHESIOLOGY annual meeting in Boston.

The results show a three to seven day course of ketamine made the headaches much less severe for almost three out of four patients.

On a scale of zero to 10, the average pain rating more than halved - from 7.5 at admission compared to 3.4 on discharge.

Dr Eric Schwenk, director of orthopaedic anaesthesia at Thomas Jefferson University Hospital, Philadelphia, said: "Ketamine may hold promise as a treatment for migraine headaches in patients who have failed other treatments."

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Ketamine is commonly used for pain relief and increasingly as an anti-depressant.

The study found that almost three quarters experienced an improvement in their migraine intensity after inpatient treatment with ketamine, which involved regular infusions of the drug after being fitted up with a drip.

Glass capsules containing ketamine

Ketamine is used to induce general anaesthesia but lower doses also provide powerful pain control for patients with many conditions.

Dr Schwenk said: "Our study focused only on short-term relief, but it is encouraging that this treatment might have the potential to help patients long term.

"Our work provides the basis for future, prospective studies that involve larger numbers of patients."